Diamond is an allotrope of carbon exhibiting a crystallographic network comprising exclusively of covalently bonded, aliphatic sp.sup.3 hybridized carbon atoms arranged tetrahedrally with a uniform distance of 1.545 .ANG. between atoms. Diamond is extremely hard having a Mohs hardness of 10. It exhibits four times the thermal conductivity of copper and it is electrically insulating. Its hardness and thermal properties are but two of the characteristics that make diamond useful in a variety of industrial components.
Abrasive particles, such as diamond particles, have been extensively used for cutting, grinding, lapping and polishing in metal removing industries as well as in medical fields such as dentistry and surgery. Abrasive particles are used in abrasive tools such as grinding and dressing wheels, crowns and single point tools. Considerable amount of research has gone into improving the bonding properties of diamond to the matrices of these tools since poor bonding at the diamond/matrix interface leads to dislodgement of the diamond particle from the matrix during the abrading operation. As a result of this research, it is known in the art that the metal coating of abrasive particles improves the retention of such particles in the matrices of various abrasive tools, such as resin bonded wheels. In particular it is known that the retention of diamond particles is improved with nickel coating. By applying a rough textured nickel coat having jagged edges, the metal coated particles provide mechanical interlocking means to retain the abrasive particles during the abrading operation. The metal coat also provides means for evenly transfering heat generated along the surfaces of the abrasive particles during the abrading action. However metal layers have poor adhesion to diamond.
It is also known in the art that the retention of diamonds in the abrasive tools is further improved by providing the particles with multiple layers of metals, such as molybdenum, titanium, niobium, chromium, zirconium, copper and nickel.
The metal coating of the particles may be achieved by a variety of methods depending on the nature of the metal coating. The metal coating may be applied under high temperature, by well known processes, such as chemical vapor deposition, molten salt deposition and powder agglomeration coating. The main drawback of such techniques is that the high process temperatures can significantly degrade the abrasive particles. The aforementioned problem of degradation may be somewhat obviated by electrolytically, electrolessly or vacuum depositing the metal coating on abrasive particles, however the problem of poor adhesion to diamond still remains.
The present invention is directed to improving adhesion of metal coats to the surfaces of diamond particles.
In addition to aforementioned diamond particles, the present invention is also directed to an article that combines the features of a heat exchanger and a printed circuit board. Printed circuit boards have become the dominant vehicle for mounting and interconnecting electronic components used for manufacturing a desired electronic circuit that generates significant degree of heat. The printed circuit board usually comprises a sheet of a dielectric substrate constructed from a chemical vapor deposited diamond film. The substrate is provided with a pattern of thin metal layer which functions as a conductive path on one or both sides. The paths or "tracks" are usually formed of a conductive material such as copper, palladium, nickel or gold. The traces collectively define all of the electrical connections between components on the board, and are routed between the locations on the board.
Diamond films are suitable for printed circuit board substrates because of their high electrical resistance, heat resistance, dimensional stability, and exceptional heat conductivity. However, diamond substrates are not easily provided with a strongly adherent metal trace. The printed circuit, i.e., the plated metal conductive path, can be damaged or separated from the substrate during the subsequent manufacturing steps or during use of the circuit board.
Additionally metal coated diamond films have also been used as heat sinks for electrical components that generate significant amount of heat.